The present invention relates in general to packet radio systems and more particularly, the invention relates to a method and an arrangement for broadcasting group messages in a packet radio network, preferably a mobile packet radio network, such as GPRS.
Mobile communication systems have been developed because it has been necessary to be able to reach people even when they are not close to a fixed telephone terminal. As the use of different data transmission services in offices has increased, different data services have also been introduced into mobile communication systems. Portable computers enable efficient data processing everywhere the user moves. Mobile communication networks in turn provide the user with an efficient access network to actual data networks for mobile data transmission. In order to realize this, different new data services are designed for existing and future mobile communication networks. Digital mobile communication systems, such as the pan-European mobile communication system GSM (Global System for Mobile Communication), support particularly well mobile data transmission.
General Packet Radio Service (GPRS) is a new service in the GSM system, and it is one the items of the standardization work of the GSM phase 2+ in ETSI (European Telecommunication Standard Institute). The GPRS operational environment consists of one or more sub-network service areas, which are interconnected by a GPRS backbone network. A sub-network comprises a number of packet data service nodes, which are referred to as GPRS support nodes (or agents) in this context, each packet data service node being connected to a GSM mobile communication network in such a manner that it is capable of providing a packet data service for mobile data terminal equipment via several base stations, i.e. cells. The intermediate mobile communication network provides circuit switched or packet switched data transmission between a support node and mobile data terminal equipment. Different sub-networks are connected to an external data network, such as a public switched packet data network PSPDN. The GPRS service thus produces packet data transmission between mobile data terminal equipment and external data networks, a GSM network acting as an access network. One aspect of the GPRS service network is that it operates almost independently of the GSM network. One of the requirements set for the GPRS service is that it must operate together with external PSPDNs of different types, for instance with the Internet or X.25 networks. In other words, the GPRS service and a GSM network should be capable of serving all users, irrespective of the type of data networks they want to register in via the GSM network. This means that the GSM network and the GPRS service have to support and process different network addressing methods and data packet formats. This data packet processing also comprises the routing the packets in a packet radio network. In addition, the users should be able to roam from a GPRS home network to an external GPRS network, the operator of which has a backbone network that may support a protocol (for instance CLNP) that is different from the one supported by the home network (for instance X.25).
Referring to FIG. 1, a typical arrangement in a GPRS network will now be described. It should be understood that the architecture of GPRS systems is not as advanced as that of GSM systems. Therefore, all GPRS terms should be interpreted as being descriptive rather than limiting terms. A typical mobile station constituting mobile data terminal equipment consists of a mobile station MS in a mobile communication network, and a portable computer PC connected to the data interface of said mobile station MS. The mobile station MS may be for instance a Nokia 2110, which is manufactured by Nokia Mobile Phones Ltd., Finland. By means of a PCMCIA-type Nokia Cellular Datacard, which is manufactured by Nokia Mobile Phones Ltd., the mobile station can be connected to any portable PC which is provided with a PCMCIA card location. The PCMCIA card thus provides the PC with an access point, which supports the protocol of the telecommunication application used in the PC, for instance CCITT X.25 or Internet Protocol IP. Alternatively, the mobile station may directly provide an access point which supports the protocol used by the PC application. Furthermore, it is possible that the mobile station MS and the PC are integrated into a single unit within which the application program is provided with an access point supporting the protocol used by it. An example of such a mobile station with an integrated computer is the Nokia Communicator 9000, also manufactured by Nokia Mobile Phones Ltd., Finland.
Network elements BSC and MSC are known from a typical GSM network. The arrangement of FIG. 1 includes a separate support node SGSN (Serving GPRS Support Node) of the GPRS service. This support node SGSN controls certain operations of the packet radio service on the network side. Such operations comprise logging on and off the system by the mobile stations MS, routing area updates of the mobile stations MS, and routing of data packets to their correct targets. Within this application, the concept of xe2x80x9cdataxe2x80x9d should be understood broadly to cover any information transferred in a digital communication system. Such information can comprise speech coded into digital form, data transmission between computers, telefax data, short segments of program code, etc. The SGSN node can be located at a BTS or at a BSC or at an MSC, or it can be located separately from any of these elements. The interface between a SGSN node and the Base Station Controller BSC is called a GB interface.
In a GPRS system the term xe2x80x9cgroupxe2x80x9d is used to refer to a plurality of mobile stations MS that are registered with a common International Mobile Group Identifier (IMGI). A message that is to be sent to all members of a group is called a xe2x80x9cgroup messagexe2x80x9d. There can be open groups and closed groups but the present invention is equally applicable to both types of groups.
Two types of Point-To-Multipoint (PTM) services are defined in GPRS:
PTM-Multicast (PTM-M); and
PTM-Group (PTM-G).
For controlling transmissions of Point-To-Multipoint messages, a GPRS system typically comprises a Point-To-Multipoint Service Center, PTM-SC, also known as a PTM server.
PTM-M is a service for broadcasting data sent by a service provider over a geographical area, such as a city. The geographical area for which a PTM-M message is destined can be defined in the message from the service provider to the PTM server PTM-SC. PTM-M service supports neither secure delivery nor security of data. This means that anyone sending messages using PTM-M service cannot be sure that the message will be delivered to the receiving party. Due to the nature of the PTM-M service, anyone can listen to it, and therefore, no data security is guaranteed.
In PTM-G transmission the delivery can optionally be secure and the data are ciphered. (The current understanding is that the SGSN establishes a connection similar to Point-To-Point (PTP) with each mobile station which has a group registration in the geographical area). The security of the transmission is the same as over the Point-To-Point connection.
Thus in prior art packet radio systems, the same PTM-G message will be sent X times if there are X subscribers in a certain routing area. It can be noted that with the increasing use of PTM-G transmissions, a large amount of traffic will be generated over the air interface of packet radio systems.
Based on the foregoing description, it is an object of the present invention to create a method and an arrangement for PTM-G message transmission that do not suffer from the above drawbacks. The object of the invention will be achieved with a method and an arrangement which are characterized by what is disclosed in the appended independent claims. Advantageous embodiments of the present invention will be presented in the dependent claims.
The invention is based on the idea of sending a PTM-G group message over a combination of broadcast and point-to-point (PTP) connections. When the message is broadcast, it is sent in a way similar to the way the PTM-M message is sent (i.e. broadcast) but in a ciphered form. A selection algorithm will be used to determine the optimal transmission mode (broadcast or point-to-point transmission). Broadcast transmission will be used if it is determined that this mode of transmission loads the network less than point-to-point transmission. In a simple embodiment of the algorithm, the number of those group members in the destination area of the group message that have not yet received the group message will be compared to a predetermined (not necessarily fixed) threshold. If the number of these remaining group members exceeds this threshold, broadcast transmission will be used, possibly with a few repetitions. Unlike the current PTM-M recommendations, the group message will be preferably acknowledged by the mobile stations that receive the message correctly. Then the group message can be sent to the remaining mobile stations via PTP connections like in prior art methods and systems.